Emulsified asphalt penetration pavement and process of constructing the same



Oct. 25, 1932. c. L. McKEssoN' 1,884,795

EMULSIFIED ASPHALT PENETRATION PAVEMENT AND PROCESS OF CONSTRUCTING THE'SAME Filed Dec. 29, 1928 r11/antw Patented Oct. 25, 1932 UNITED STATES PATENT OFFICE CLAUDE L. MCKESSON, OF OAKLAND, CALIFORNIA, ASSIGNOR `TO AMERICAN BITUMULS COMPANY, OF SAN FRANCISCO, CALIFORNIA, A. CORPORATION F DELAWARE EMULSIFIED ASPHALT PENETRATION PAVEMENT AND PROCESS OF CONSTRUCTING" THE SAME Application filed December' 29, 1928. Serial No. 329,302.

My invention relates to the construction of a bituminous pavement somewhat resembling hot asplialtic penetration macadam but which isy free from defects inherent to that type and which embodies all of the superior qualities usually found only on hot plant mixed asphalt concrete pavement.

More specifically the objects which I accomplish are the elimination of large voids particularly in the lower portion of the pavement and excesses of bituminous binder which necessarily results from the use of coarse rock and hot asphalt inthe first course of the penetration type as heretofore constructed. These unavoidable defects frequently lead to i the failure of the pavement. By my method of construction I secure a dense pavement of interlocking stone particles each` of which is uniformly coated with a thin eiicient thickness of pure asphalt binder. The under side of my pavement is thoroughly and efficiently sealed against the ent-rance of moisture or mud from subgrade and the surface of the pavement is likewise sealed to prevent the entrance of moisture falling on the surface.

The foregoing 'and other beneficial results are attained in the following manner:

by reference to the following description and to the accompanying drawing in which Fig. 1 represents a section of pavement during the first stage of construction, in which (l) indicates the subgrade which, may be of earthy material, brought to vgrade and compacted, (2) shows a layer of stone dust or ine sand, and (3) a layer of crushed rock or gravel graded from maximum to minimum preferably with exclusion of nes.

Fig. 2 shows the second stage of construction in which the numerals (l), (2) and (3) arethe same as above except that the layer of crushed rock (3) is shown coated with bituminous emulsion. The numeral'(4) indi- Cates a. layer of bituminous emulsion collected and lying on the layer of stone dust (2). ,The numeral (5) indicates a top coating of screenings placed on the graded aggregate (3) after the application of the bituminous emulsion.

Fig. 3 shows the completed pavement, the

corresponding numerals beingv the same as in Fig. 2. In this figure is illustrated the final seal coat (6) which consists of an application of Portland -cement or stone dust swept into the interstices of the compacted screenings (5) and covered with bituminous emulsion.

The first stage 'in the production of this new and novel type of pavement is the placing on the subgrade of a thin layer (2) of stone dust and stone chips or of sand, preferably ine. On this is spread a layer of crushed rock or gravel (3) having an uncompacted thickness of one fifth to one third more than the desired finished thickness of the pavement to'be built. This crushed rock or gravel is graded in size from a maximum to a minimum. The maximum size is not arbitrarily xed except that the largest dimension of the coarse particles lshould not exceed three fourths of the finished thickness of the pavement. The minimum size of particles is very important. Particles which pass a U. S. standard lOniesh sieve are excluded where best results are to'be secured. In usual practice material is not used which will not pass ascreen having circular openings of a diampaveiiient. The grading between the maximum limit selected and the minimum size limit as above set forth which is most satisfactoryis one which will reduce the voids to a minimum. UsuallT the voids can be brought I of half of the finished thickness of the c I My invention will be clearly understood' During the blading and cultivating operations, stone dust or dirt which may have remained in the material falls to the bottom. The surface of the material is then shaped with a blade to conform with the Vfinished contour of the road. After the l aded crushed rock or gravel is thus prepare bituminous binder in the form of an aqueous asphaltic emulsion is applied in suiicient quantity to entirely penetrate and permeate the layer of graded crushed rock or gravel (3) and with some excess (4) which collects beneath this material on the layer of stone dust and chips or sand rst placed.

The character of this emulsion is essential to the successful construction of my pavement. A suitable emulsion must have a very low viscosity, preferably less than a specific viscosity of two (Engler). Such emulsions are now made commercially using asphalt and water with small additions of caustic soda, oleic acid or other emulsifying agents, but to my knowledge emulsions were not used in the construction of the type herein described prior to my invention. A desirable emulsion should contain fifty per cent 0r more of asphalt, the remainder being water and emulsifying agent.

The emulsion is preferably applied with pressure distributors in two or more applications. The amount required is usually about one-half gallon per square yard per inch of finished thickness, assuming theeniulsion to have an asphalt content about as stated above.

After the emulsion has been applied the surface of the pavement is lightly covered with screenings (5) and is then rolled with a suitable roller until it is fully compressed and until it is firm and unyielding. During the first rolling soon after the emulsion has been spread, the pavement is plastic under the roller and is readily shaped to the desired contour. Usually the final rolling cannot be done until one or more days after the emulsion has been spread, the lapse of time being necessary to allow the emulsion to break or set. A

After the pavement thus constructed has been fully and finally compacted it isgiven a seal coat (6). This consists of an application of Portland cement or stone dust swept into the interstices in the surface of the pavement and then covered with a light application of emulsified asphalt. Portland cement is preferable for the seal coat because it quickly draws moisture ynecessary for hydration from the emulsion thereby breaking the emulsion. The Portland cement hardens in the interstices into which it has been swept, renders the pavement waterproof and at the same time prevents subsequent displacement of rock particles in the surface of the pavement. Stone dust if used also takes moisture from the emulsion'and in time absorbs the surplus asphalt in the seal coat. The amount of Porland cement or stone dust used is the amount which can be swept, into surface interstices in the pavement and varies under different conditions.

It will be noted that this pavement diii'ers from usual penetration macadams in that it does not use different sizes of stone in successive layers beginning with large stone openly graded, followed by key rock, etc. It also has a distinct advantage and eects great economy in that hand labor is almost entirely eliminated. It has the additional advantage of greater smoothness because of its plasticity when rst rolled. High spots, bumps and low s ots are corrected by rolling at thisstage. ith types heretofore used, itis well known that irregularities of this kind cannot usually be eliminated by rolling but must be avoided by careful correction after the irst rolling and before hot asphalt has been applied.

The thickness of a pavement constructed according to my method is limited only by the ability of the roller to properly compress the rock. In a test I have readily enetrated one foot of material graded from 1% mesh to 10 mesh with emulsion and have fully coated the particles with asphalt. Such material is finer, as to maximum size, than would generally be used.

The pavement herein described o'ers anadded economyk in that it utilizes the entire product of the `crushe1= ranging from the maximum size to stone dust.

The mat formed on the bottom of the pavement consisting of stone dust and asphalt effectively prevents mud and water from entering the pavement from the under side, a common cause for failure in ordinary penetration macadams in which the coarse base stone is usually poorly filled with screenings due to the inability to get screenings' through'the carpet of hot asphalt which co1- lects in the upper interstices base stone.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

l. A pavement consisting of stone particles graded from maximum to a minimum size which excludes material passing a ten mesh sieve screen, a coating of emulsitied asphalt on the stone particles and a seal coat of stone dust and asphalt emulsion on the under side of said pavement.y

2. A pavement consisting of a layer of emulsified asphalt covered stone dust and 7 screenings adjacent to the subgrade, a layer of compressed stone above said layer of stone dust, forming the main body of said pavement, said compressed stone being graded in size from a maximum and substantially free from lines to a minimum, and a coating ot emulsiiied. asphalt on said stone particles.

f 3. The process of constructing a pavement comprising placing a layer of stone dust and screenings upon a subgrade, upon this placing a layer of crushed rock graded from a maximum to a minimum size, composing the main body of the pavement, penetrating the said crushed rock with an aqueous emulsion of asphalt, a portion of which is allowed to pass through the crushed rock and collect on the stone dust beneath forming thereby an under seal, and finally rolling the crushed rock until it is firm and unyielding.

4. The process of constructing a pavement comprising placing a layer of stone dust and screenings upon a subgrade, upon this placing a layer of crushed rock graded from a maximum to a minimum size, composing the main body of the pavement, penetrating the said crushed rock with an aqueous emulsion of asphalt, a portion of which is allowed to pass through the crushed rock and collect on the vstone dust beneath forming thereby of mineral aggregate an under seal, rolling the crushed rock until it is firm and unyielding, applying a seal coat consisting of Portland cement suflicient in quantity to lill interstices in the surface ,of the pavement and finally coating the surface with emulsiied asphalt.-

5. The process of constructing a pavement comprising placing a layer of road material graded from a maximum size to a minimum size which excludes all material passing a ten mesh screen, of penetratin the said material with an aqueous emulsion, a portion of which is allowed to passthrough the ma-l terial and collect beneath ormin an under seal, rolling the materia until it is lirm and unyielding, finally applying a seal coat consisting of Portland cement sulficient in quantity to fill interstices in the surface of --the pavement and by coating the surface With emulsied asphalt. 6. The process of constructin a pavement comprising placing a layer of ne road material on a subgrade, placing thereon a layer substantially free from fine material, applying to the surface thereof an aqueous emulsion of bituminous binder in quantity suicient to coat the aggregate and collect on the tine material beneath, thereby forming an under seal, and inally compacting the coated aggregate.

7. The process of constructin a pavement comprising placing a layer of ne road material on a subgrade, placing thereon a layer thereby of mineral aggregate substantially free from fine material, applying to the surface thereof an aqueous emulsion of bituminous binder in quantity suiicient to coat the laggregate and collect on the line material beneath, therebyforming an under seal, compacting the coated aggregate until 'firm and unyielding, and finally applying a top seal of 511e road material and emulsited bitumen..

8. The process of constructing a avement which comprises placing a layer o' mineral aggregate substantially free from material passing a ten mesh screen, applying to the surface thereof an aqueous emulsion of bi- 4tuminous binder in quantity sufficient to coat the aggregate and collect beneath, thereby forming an under seal, compacting the aggregate until firm and unyielding, applying a seal coat of line road material in quantity Sullicient to fill interstices in the surface, and finally coating the surface with emulsiiied bitumen. v

9. A pavement comprising mineral aggregate substantially free from fine materlal, a coating of emulsiied bitumen on said mineral aggregate and a seal coat of emulsified bitumen and fine material on the under side of said pavement.

10. A pavement comprising graded mineral aggregate substantially free from fine material, a coating of emulsified bitumen on said mineral aggregate, a seal coat of emulsiied bitumen on the underside of said pavement and a seal coat of line road material and emulsified bitumen on the surface.

CLAUDE L. MCKESSON.

` CERTIFICATE OF CORRECTION.

Patent No. 1,884, 795. October 25, 1932;

CLAUDE L. MCKESSON.

, lt is hereby certified that error-appears in the printed specification ofthe above numbered patent requiring correction as follows: Page 2, line 123, claim 2, strike out the words "to a minimum" and insert the same after the word "maximum", in line 122; page 3, lline 32, claim 5, strike out the word "finally", and line 35, for "by" read "tinally"; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 24th day of January A. D.l 1933.

M. I. Moore,

(Seal) Acting' Commissioner oi Patents. 

